Method and device for regenerating a particulate filter for exhaust line, and adapted particulate filter

ABSTRACT

The invention relates to a method of regenerating an exhaust line particle filter wherein particles lining the walls of the filter are heated to a temperature higher than their combustion temperature, which method is characterized in that: the heat necessary to heat said particles is produced by adding to a solid first compound present in a reactor a gaseous second compound adapted to combine with said first compound to form a solid third compound by way of an exothermic reaction, and the heat resulting from the combustion of said particles is used to regenerate said solid first compound and said second compound by way of an endothermic reaction that is the opposite of said exothermic reaction. The invention also relates to an exhaust line and a particle filter for implementing the above method.

The invention relates to the automotive industry. To be more precise, itrelates to regenerating particle filters used on diesel engine exhaustlines of vehicles of recent design.

Diesel-engined automotive vehicles of recent design have their exhaustline equipped with particle filters (PF) to reduce emission of solidpollutants. Soot collects on the PF walls and must be eliminatedregularly to prevent the PF clogging and to return it to its nominalefficiency. Also, clogging of the PF progressively creates aback-pressure that is harmful to proper operation of the engine. Thesoot may be eliminated by heating the filter to a temperature higherthan the combustion temperature of the soot (which is normally around550° C.) by means of the exhaust gas flowing therein. To this end, themost widespread technical solution consists in:

adding to the fuel, for example when filling the tank, an additive suchas ceria whose function is to reduce the combustion temperature of thesoot to around 450° C.; and

periodically post-injecting fuel into the exhaust line on the upstreamside of the PF, which heats the exhaust gas to a temperature sufficientto ignite the soot (450° C. or higher).

The above technique has the following drawbacks.

Firstly, it consumes energy, since post-injection leads to increasedfuel consumption.

Secondly, during PF regeneration phases, the combustion of thepost-injected fuel is particularly unstable and requires conditions ofengine load and fluid temperature that can be difficult to achieve undercertain climatic or operating conditions. If combustion is incomplete oruncontrolled, it leads to the emission of pollutant gas and consumesoxygen, with the risk of defective combustion of the soot followingpost-injection of fuel. It is therefore possible for post-injection tohave the effect opposite to that required, and good management ofpost-injection makes it necessary to find compromises. Management ofpost-injection has to be refined and controlled, and achieving this hasproved to be particularly complex.

Another solution for PF regeneration is heating to a temperature higherthan the soot combustion temperature by means of electrical heatingelements. However, that solution is costly in terms of energy, as isheating the exhaust gas by electrical heating elements. Moreover,heating the filter causes thermal gradients within the filter whicheventually accelerate its deterioration.

Moreover, the ceria used to reduce the soot combustion temperatureconstitutes an impurity in itself, tending to block the passages of thePF. This makes it necessary to remove and clean the filter about every80 000 kilometers (km).

The object of the invention is to propose a method of regenerating aparticle filter that is simple to use, effective, economic in terms ofenergy, and does not have the drawbacks associated with post-injectionof fuel referred to above.

To this end, the invention consists in a method of regenerating aparticle filter for an internal combustion engine exhaust line, whereinparticles lining the walls of the filter are heated to a temperaturehigher than their combustion temperature, which method is characterizedin that:

the heat necessary to heat said particles is produced by adding to asolid first compound present in a reactor a gaseous second compoundadapted to combine with said first compound to form a solid thirdcompound by way of an exothermic first reaction, and

the heat resulting from the combustion of said particles is used toregenerate said solid first compound present in said reactor and saidgaseous second compound by way of an endothermic second reaction that isthe opposite of said exothermic first reaction.

The heat to be imparted to the particles to heat them and the heat to beimparted to the solid third compound to regenerate the solid firstcompound can be transmitted through the walls of the particle filter orvia the exhaust gas flowing along said exhaust line.

In a preferred but not exclusive embodiment of the invention, said solidfirst compound is lime (CaO) and said second compound is steam.

The invention also consists in an internal combustion engine exhaustline of the type including a particle filter and means for regeneratingit adapted to heat particles lining the walls of the filter to atemperature greater than their combustion temperature, which exhaustline is characterized in that said means comprise:

a reactor containing a solid first compound;

an evaporator for vaporizing a second compound able to combine with saidsolid first compound to form a solid third compound by way of anexothermic reaction;

means for establishing communication between said evaporator and saidreactor on command;

means for communicating to said particles the heat generated bycombining said first and second compounds;

means for communicating to said solid third compound the reaction heatgenerated by the combustion of said particles so as to causeregeneration of said first and second compounds during said combustion;

means for collecting said second compound in gaseous form during saidregeneration of the first and second compounds and for transmitting itto a condenser for liquefying it; and

means for establishing communication between said condenser and saidevaporator on command.

A reactor containing the solid first compound may be integrated into theparticle filter.

A reactor containing the solid first compound may be placed against theoutside wall of the exhaust line.

Said means for communicating to said solid third compound the reactionheat generated by the combustion of said particles may include a heatpipe for collecting heat from the exhaust gas on the downstream side ofthe particle filter.

Said reactor containing said solid first compound may be placed insideor outside the exhaust line on the upstream side of the particle filteron the normal path of the exhaust gas and the means for communicating tosaid solid third compound the reaction heat generated by the combustionof said particles may include branch pipes and valves for modifying thepath of the exhaust gas in such a manner as to place said reactor thatis on the downstream side of the particle filter on the path of theexhaust gas during regeneration of the first and second compounds.

Said reactor containing said solid first compound may be placed insideor outside the exhaust line on the downstream side of the particlefilter and may include a heat pipe for transmitting heat generated bycombining said first and second compounds to the particle filter and/orto the exhaust gas on the upstream side of the particle filter.

The exhaust line may include means for detecting clogging of theparticle filter and for triggering regeneration of said particle filter.

It may include means for detecting initiation of the reaction ofcombustion of the particles lining the filter and for triggering theestablishing of communication between said reactor and said condenser.

The invention also consists in a particle filter for an internalcombustion engine exhaust line, characterized in that it includes areactor situated away from the path of the exhaust gas and containing asolid first compound able to react with a second compound by way of areversible exothermic reaction in such manner as to heat the walls ofsaid filter to a temperature greater than the combustion temperature ofparticles said filter is intended to capture.

A reactor may be placed around said filter and/or integrated into saidfilter.

Clearly, the invention is based on combining a particle filter (PF) anda thermochemical reactor capable of increasing the temperature of a heatsource by means of a solid-gas reaction. The reactor is used to heat thePF or the exhaust gas to a temperature higher than the soot combustiontemperature. To this end, a solid reagent X combines in the reactor witha gas G initially contained in partly liquid form in an evaporator byway of a reversible exothermic reaction X+G→XG+heat. This generation ofheat increases the temperature of the PF or the exhaust gas sufficientlyfor combustion of the soot. Since that combustion is exothermic, itcontributes wholly or in part to regenerating said first and secondcompounds by decomposing the solid third compound XG. The minimumtemperature to which the compound XG must be heated during itsdecomposition is a function of the vapor pressure of the compound Gobtained when communication is established between said reactor and saidcondenser, in which the compound G is recovered in the liquid state. Thecompound G in the liquid state is periodically sent to the evaporatorand is then ready to participate in further regeneration of the PF.

The invention will be better understood on reading the followingdescription, which is given with reference to the appended drawings, inwhich:

FIG. 1 is a diagram showing in longitudinal section the components of aportion of an exhaust line equipped with one embodiment of a device ofthe invention when idle;

FIG. 2 shows a portion of the FIG. 1 exhaust line in cross section takenalong the line II-II;

FIGS. 3 to 6 show the operation of this embodiment of the device of theinvention in its successive configurations;

FIG. 7 shows a second embodiment of a device of the invention; and

FIGS. 8 a, 8 b show a third embodiment of a device of the invention.

A particle filter for a diesel engine exhaust line consists of a ceramicelement having a multiplicity of passages, for example an element madeof silicon carbide (SiC). Soot resulting from combustion of the fuel isretained on the walls of the passages. The filter can withstand hightemperatures, of the order of 1200° C., encountered locally on itsinside walls when the soot is combusted to regenerate the filter. As ageneral rule, regeneration is required every 400 km to 500 km, althoughthis distance can obviously vary as a function of the quality of thefuel used, the conditions of use of the vehicle, and the adjustments ofthe engine.

The exhaust line 1 shown partly in FIG. 1 is equipped with a PF 2 of theabove kind including a multiplicity of passages 3 through which exhaustgas to be cleansed of its solid pollutant particles flows, as shown bythe arrow 4, this gas arriving from the upstream portion of the line 1(that on the right-hand side in FIG. 1).

According to the invention, the portion 5 of the exhaust line in whichthe PF 2 is installed includes a reactor disposed around the PF 2, andalso in place of the central region of the PF 2 (and thus integratedinto the PF 2), the reactor containing a reagent 6 consisting of a solidfirst compound having the following properties under the relevantconditions of temperature and pressure:

at the usual temperature of the exhaust gas (which is generally of theorder of 150-250° C.), the solid first compound is able to absorb agiven second compound that is in the gaseous state at the sametemperature, but that is able to condense under normal or readilyobtainable conditions of temperature and pressure, said absorptionreaction being strongly exothermic and therefore able to heat the sootcoating the walls of the passages 3 of the PF 2 to a temperature higherthan their combustion temperature, and

because of the effect of the heat generated by combustion of the soot,the solid first component is regenerated in its original state by theendothermic reaction that is the opposite of the previous reaction, saidgaseous second compound being released in order to be condensed.

A preferred example of the solid first compound is lime (CaO), becauseis able to react with steam by the following reversible reaction:

It is this combination CaO/H₂O that is considered by way of example inthe remainder of the description, although this must not be regarded aslimiting the invention.

According to the invention, the device for regenerating the PF 2comprises:

a condenser 7 external to the line 1 and which, when the system is idle,contains water 8 in the liquid state;

an evaporator 9 inside the line 1, on the upstream side of the PF 2, andwhich can selectively communicate with the condenser 7 via a pipe 10including a valve 11 that is closed when the system is idle;

a branch pipe 12 connected to the evaporator 9 and including a valve 13that selectively allows steam present in the evaporator 9 when thedevice is operating to be directed onto the lime CaO 6 situated at theperiphery and at the centre of the PF 2 and is closed when the system isidle; and

two branch pipes 14, 15 connected to the pipe 12 on the downstream sideof the valve 13; the pipe 14 can feed steam onto the lime CaO 6, orextract it therefrom during regeneration steps, preferably by means of amultiplicity of branch connections 16, 17, 18, to guarantee ashomogeneous a distribution of the water as may be desirable in thereaction area, as well as equally homogeneous extraction of water duringsteps of regenerating the lime CaO 6 in the reactor; the pipe 15 conveyssteam extracted from the reaction area to the condenser 7; a valve 19 onthe pipe 15 controls the entry of steam into the condenser 7.

When the installation is idle, it may be in the configurationrepresented in FIG. 1, with water 8 present in the condenser 7 in theliquid state and all the valves 11, 13, 19 closed (and thus shown blackin FIG. 1).

If the installation is required to be operational quickly, the valve 11is opened (see FIG. 3, in which the open valve 11 is shown white) andwater 8 is sent to the evaporator 9 (arrow 20). This transfer can beeffected by a pump or simply by gravity if the configuration of theinvention allows this. Once the transfer has been completed, the valve11 is closed and the water 8 present in the evaporator 9 is heated tothe temperature of the exhaust gas flowing around the evaporator. Thewater 8 is advantageously transferred into the evaporator 9 when thevehicle is stopped, the temperatures of the condenser 7 and theevaporator 9 tending to equalize. This situation is symbolicallyrepresented in FIG. 3 by the lack of any arrows 4 representing the flowof exhaust gas.

The installation is in the state represented in FIG. 4 when the vehicleis moving. All the valves 11, 13, 19 are closed and all the water 8 isin the evaporator 9, in liquid-vapor equilibrium, and therefore at thesaturation vapor pressure, for example 5 bar to 35 bar, depending on thetemperature of the exhaust gas, (150° C. to 250° C.).

Regeneration of the PF can begin from the above state.

This operation can be started at the initiative of the driver orautomatically. The triggering time can be determined systematically as afunction of the distance traveled since the last regeneration cycle.Triggering can also be decided on because appropriate sensors indicatean abnormally high head loss of the exhaust gas between the upstream anddownstream sides of the PF 2, indicating clogging of the passages 3 ofthe PF 2.

Once a regeneration operation has been decided on, the installation isplaced in the configuration shown in FIG. 5. The valves 11, 19 remainclosed and the valve 13 is opened, with the result that steam 8 isdirected onto the lime CaO 6 and absorbed thereby to effect theexothermic reaction:CaO+H₂O→Ca(OH)₂+ΔH

The heat generated is communicated to the soot deposited in the passages3 via the walls of the PF 2, the parameters of the installation beingchosen so that the soot is heated to a temperature higher than itscombustion temperature, in order to initiate combustion. In particular,the steam pressure must be sufficient. In this way the passages 3 of thePF 2 are cleansed of the soot coating them.

Because the combustion of the soot is exothermic, it can heat the PF 2to a temperature of 1000° C. or more. This heat is transmitted to thecalcium hydroxide 6 surrounding it. However, this temperature rise isnot essential for the system to operate, as explained above.

Combustion can be detected by measuring the exhaust gas temperaturedifference or the pressure difference between respective opposite sidesof the PF 2. At this time the configuration of the installation ischanged to that of FIG. 6, with the valves 11, 13 closed and the valve19 open. Because of the heat from combustion of the soot, steam that isgenerated by the endothermic reaction that regenerates the lime CaO 6:Ca(OH)₂→CaO+H₂O−ΔHpasses through the pipes 16, 17, 18, 14, 15 into the condenser 7, whereit condenses. The condenser 7 may be cooled by an external flow of fluidto achieve this, but simple cooling by ambient air may be sufficient.

When the reactions to regenerate the PF 2 and the lime CaO 6 arecompleted (which can be detected by comparing the temperatures of theexhaust gas on the upstream and downstream sides of the PF 2 and findingthat they have become very similar again), the valve 19 is closed andthe installation returned to the idle state described above andrepresented in FIG. 1.

Alternatively, the idle state of the installation, during which thevehicle and its exhaust line 1 operate under normal conditions, may bethe state represented in FIG. 4, in which water 8 is present in theevaporator 9 under liquid-vapor equilibrium.

The whole of the regeneration of the PF 2 between the start of admissionof steam 8 into the CaO 6 and the returning of all the steam 8 to thecondenser 7 can take approximately one minute, or even less.

Compared to existing PF regeneration installations, the installation ofthe invention has the very significant advantage of limiting, or eveneliminating, input of external energy apart from the entirely negligibleamount of energy needed to operate the valves 11, 13, 19 and the sensorsfor determining the favorable times for triggering the various steps ofthe cycle. This is possible because the chemical reactions employed are“self-maintaining”, as it were, the heat from the exothermic reaction ofhydration of the lime CaO triggering the exothermic reaction ofcombustion of the soot, the reaction heat of which in turn triggers theendothermic reaction of dehydrating the hydroxide Ca(OH)₂.

In particular, post-injection of fuel is not necessarily useful forregenerating the PF 2. It is even possible, if the variouscharacteristics of the installation are appropriate, to dispenseentirely with the addition of ceria to the fuel, provided that the heatgiven off by hydration of the lime CaO 6 is sufficient to achieve atemperature sufficiently high to initiate combustion of the soot. Theinstallation is then particularly economical to use.

It will also be noted that regeneration is effected without usingmaterials that are hazardous to the environment and does not in itselfproduce any polluting compounds.

As the combination of the PF 2 and the reactor is placed in a casing 20that is open only where it faces the components of the PF 2 and thepassages for the pipes 16, 17, 18, the lime CaO 6 is not on the path ofthe exhaust gas and does not come into contact with them. It istherefore not poisoned by impurities present in the fuel (for examplesulfur).

Mixing the lime CaO 6 with a material that is a good conductor of heat,such as expanded graphite, is recommended to improve heat transfer withthe PF 2. This material also has the advantage of being porous and thusof allowing the steam to pass through the lime CaO 6.

The configuration of the PF 2 and its environment shown by way ofexample in FIGS. 1 to 6 is advantageous in that the PF 2 is heated bothfrom the inside and from the outside by the lime CaO 6 during thehydration reaction, and conversely the lime 6 in the hydrated state iseverywhere relatively close to the heat source represented by the PF 2when heated during the combustion of soot. For these reasons, theefficiency of the heat transfers and the progress of the chemicalreactions resulting therefrom can be optimized. However, it would remainwithin the spirit of the invention to dispose the lime CaO 6 only aroundthe PF 2 or only at the centre of the PF 2. Conversely, a plurality of“rods” of lime CaO 6 could be disposed inside the PF 2 instead of asingle one as in the example shown. Generally speaking, disposing thelime CaO 6 in multiple locations of the PF 2 minimizes temperaturegradients inside the PF 2 and therefore the mechanical stresses to whichit is subjected.

Another alternative to the configuration shown would be to move theevaporator 9 to the downstream side of the PF 2 or out of the exhaustline 1 and into contact with its outside wall. This avoids thepossibility of disturbing the gas flows inside the PF 2.

Integrating the reactor containing the lime CaO 6 with the PF 2 itselfand/or its immediate environment has the advantages as stated above, butis not without drawbacks, however. The heat produced by the variouschemical reactions is consumed in part to heat the walls of the PF 2 andnot to heat the soot or the hydrated lime 6 directly. Also, some of thisheat is evacuated by the exhaust gas flow and is not recovered by thesoot or the hydrated lime 6 either. Obtaining satisfactory results maytherefore lead to increasing the external dimensions of the exhaust linesignificantly relative to what is usual. Also, it is necessary toredesign completely the exhaust line in the area of the PF 2, and thenecessary modifications may not be suitable for an existing line.

To overcome these drawbacks, the solution represented in FIG. 7 may beenvisaged, where the entire PF 2 regeneration reactor and itsancillaries are installed outside the exhaust line (in FIG. 7 componentswith exactly the same function as those represented in FIGS. 1 to 6 aredesignated by the same reference numbers).

In this variant, the reactor containing the lime CaO 6 is disposedoutside and around the exhaust line 1, on the upstream side of the PF 2.The evaporator 9 is also disposed outside and around the exhaust line 9,between the PF 2 and the reactor containing the lime CaO 6. Heattransfer between the exhaust gas and these two devices is thereforeeffected through the wall of the exhaust line 1. A heat pipe 21 or anyother functionally equivalent device transmits heat from the exhaust gason the downstream side of the PF 2 to the reactor containing the limeCaO 6 on the upstream side of the PF 2.

When the decision to regenerate the PF 2 has been taken, the watercontained in the evaporator 9 is fed in the form of steam into the limeCaO 6 via the pipes 12, 14, the valve 13 being the only open valve, andthe reaction heat then heats the exhaust gas to a temperature higherthan the soot combustion temperature. The combustion of the soot heatsthe exhaust gas, from which heat is recovered by the heat pipe 21, andthe fluid therein transfers the heat to the hydrated lime 6 in order toregenerate the lime CaO. This is reflected in the sending of steam intothe condenser 7, the valve 19 being the only open valve. Afterregeneration, the heat-exchange fluid in the heat pipe 21 returns to thedownstream portion thereof.

In order to be installed on an existing exhaust line, this variantrequires only sufficient free space in the environment of the PF 2 toinstall the reactor containing the lime CaO 6, the evaporator 9, thecondenser 7, and the heat pipe 21. Other advantages are that the exhaustgas heated on the upstream side of the PF 2 enters directly into contactwith the soot without requiring the PF 2 to be preheated and that theheating of the PF 2 after combustion of the soot is substantiallyhomogeneous throughout its volume, which induces lower stresses in thematerial of the PF 2.

It is clear from the above description that to regenerate the PF 2 thereactor containing the lime CaO 6 must be on the upstream side of the PF2, on the path of the exhaust gas, if it is not integrated into PF 2itself. However, during combustion of the soot, it would be preferablefor the reactor containing the hydrated lime 6 that is to be regeneratedto be on the downstream side of the PF 2, in order to be regenerateddirectly by the exhaust gas heated by the combustion of the soot. Thiscan be achieved by associating the exhaust line with a device forreversing the direction of flow of the exhaust gas through the PF 2between the reaction step and the step of regenerating the lime CaO 6.

This can be achieved by means of the installation shown in FIGS. 8 a, 8b. A PF 2 is inserted into the exhaust line 1, together with a reactorcontaining lime CaO 6, separate from the PF 2, and through which theexhaust gas can flow via appropriate perforations or pores. The reactor6 is on the upstream side of the PF 2 on the normal path of the exhaustgas. The installation also includes an evaporator, a condenser, and thepipes and valves necessary for the operation of the reactor, which aresimilar to those described for the above-described variants of theinvention and are not shown in FIGS. 8 a, 8 b. The line 1 also includestwo branch pipes 22, 23 enabling the gas not to pass directly throughthe reactor 6 and the PF 2, and two valves 24, 25 controlling routing ofthe exhaust gas either directly to the reactor 6 and the PF 2, or elseinto the branch pipes 22, 23.

When the exhaust line 1 is operating normally, the valves 24, 25 isolatethe branch pipes 22, 23 from the normal path of the exhaust gas, whichgas therefore passes successively through the reactor containing limeCaO 6 and the PF 2 (see FIG. 8 a).

When a cycle of regenerating the PF 2 is started, the valves 24, 25remain in their preceding position and steam is directed onto the limeCaO 6 from the evaporator (not shown), to cause the reaction ofhydrating the lime CaO 6, leading to heating of the exhaust gas beforeit passes through the PF 2 and to starting combustion of the soot in thePF 2.

Once combustion of the soot has started and has been detected, thevalves 24, 25 are operated so that the exhaust gas passes first throughthe first branch pipe 22, then through the PF 2, in which it is heatedby the combustion of the soot, then through the reactor containing thelime 6 in the hydrated state, so as to dehydrate it, and then throughthe second branch pipe 23, so as to be finally returned to thedownstream portion of the exhaust line 1.

When regeneration of the lime CaO 6 is completed, the valves 24, 25 arereturned to their original position and the exhaust line 1 begins tooperate under normal conditions again.

In this configuration, it is possible for the exhaust gas to entrainparticles of soot onto the casing of the reactor in which the lime 6 isbeing dehydrated. Combustion of that soot is then completed as close aspossible to the tubes containing the solid calcium oxide or hydroxide,which encourages efficient transfer of heat.

In the example described and shown in FIGS. 8 a, 8 b, the reactorcontaining lime CaO 6 is placed inside the exhaust line 1, but it wouldbe possible to place it around the line 1, as in the FIG. 7 example.

The invention is not limited to the examples described and shown. Inparticular, it would be possible to combine different variants of theinvention, in particular to place reactors containing lime CaO 6 bothinside and outside the PF 2, and generally inside and outside theexhaust line 1.

Another variant would have the reactor 6 containing the solid firstcompound inside or outside the exhaust line 1 on the downstream side ofthe PF 2 and transmit heat generated by the combination of the solidfirst compound and the gaseous second compound with the particles ofsoot directly to the PF 2 and/or to the exhaust gas on the upstream sideof the PF 2, by means of a heat pipe.

The invention has a preferred application to diesel engine exhaustlines, but may be applied to the exhaust line of any type of internalcombustion engine for which it might be deemed necessary to use aparticle filter.

1. A method of regenerating a particle filter for an internal combustionengine exhaust line, wherein: particles lining the walls of the filterare heated to a temperature higher than their combustion temperature,the heat necessary to heat said particles is produced by adding to asolid first compound present in a reactor a gaseous second compoundadapted to combine with said first compound to form a solid thirdcompound by way of an exothermic first reaction, and the heat resultingfrom the combustion of said particles is used to regenerate said solidfirst compound present in said reactor and said gaseous second compoundby way of an endothermic second reaction that is the opposite of saidexothermic first reaction.
 2. A method according to claim 1, wherein theheat necessary to heat the particles is transmitted to them and the heatnecessary to regenerate the solid first compound is transmitted to thesolid third compound through the walls of the particle filter.
 3. Amethod according to claim 1, wherein the heat necessary to heat theparticles is transmitted to them and the heat necessary to regeneratethe solid first compound is transmitted to the solid third compound bymeans of the exhaust gas passing through said exhaust line.
 4. A methodaccording to claim 1, wherein said solid first compound is lime CaO andsaid second compound is steam.
 5. An internal combustion engine exhaustline, of the type including a particle filter and means for regeneratingit, adapted to heat particles lining the walls of the filter to atemperature greater than their combustion temperature, wherein saidmeans comprise: a reactor containing a solid first compound; anevaporator for vaporizing a second compound able to combine with saidsolid first compound to form a solid third compound by way of anexothermic reaction; means for establishing communication between saidevaporator and said reactor on command; means for communicating to saidparticles the heat generated by combining said first and secondcompounds; means for communicating to said solid third compound thereaction heat generated by the combustion of said particles so as tocause regeneration of said first and second compounds during saidcombustion; means for collecting said second compound in gaseous formduring said regeneration of the first and second compounds and fortransmitting it to a condenser for liquefying it; and means forestablishing communication between said condenser and said evaporator oncommand.
 6. An exhaust line according to claim 5, wherein a reactorcontaining the solid first compound is integrated into the particlefilter.
 7. An exhaust line according to claim 5, wherein a reactorcontaining the solid first compound is placed against the outside wallof the exhaust line.
 8. An exhaust line according to claim 7, whereinsaid means for communicating to said solid third compound the reactionheat generated by the combustion of said particles include a heat pipefor collecting heat from the exhaust gas on the downstream side of theparticle filter.
 9. An exhaust line according to claim 5, wherein saidreactor containing said solid first compound is placed inside or outsidethe exhaust line on the upstream side of the particle filter on thenormal path of the exhaust gas, and the means for communicating to saidsolid third compound the reaction heat generated by the combustion ofsaid particles include branch pipes and valves for modifying the path ofthe exhaust gas in such a manner as to place said reactor that is on thedownstream side of the particle filter on the path of the exhaust gasduring regeneration of the first and second compounds.
 10. An exhaustline according to claim 5, wherein said reactor containing said solidfirst compound is placed inside or outside the exhaust line on thedownstream side of the particle filter and it includes a heat pipe fortransmitting heat generated by the combination of said first and secondcompounds to the particle filter and/or to the exhaust gas on theupstream side of the particle filter.
 11. An exhaust line according toclaim 5, including means for detecting clogging of the particle filterand for triggering regeneration of said particle filter.
 12. An exhaustline according to claim 5, including means for detecting initiation ofthe reaction of combustion of the particles lining the filter and fortriggering the establishing of communication between said reactor andsaid condenser.
 13. A particle filter for an internal combustion engineexhaust line, the particle filter including a reactor situated away fromthe path of the exhaust gas and containing a solid first compound ableto react with a second compound by way of a reversible exothermicreaction in such manner as to heat the walls of said filter to atemperature greater than the combustion temperature of particles saidfilter is intended to capture.
 14. A particle filter according to claim13, wherein a reactor is placed around said filter.
 15. A particlefilter according to claim 13, wherein a reactor is integrated into saidfilter.